1. Field of the Invention
The present invention relates generally to methods for genetically altering plant materials and reproducing plants therefrom. More particularly, the invention relates to genetic transformation of castor.
2. Description of the Art
Castor (Ricinus communis L.) is an important crop of the family Euphorbiaceae. It is a monotypic species of the genus Ricinus and has considerable economic value because of its oil-rich seeds, which yield castor oil, a strategically important oil with numerous industrial uses. The castor bean contains up to 60% oil of unique composition. Chemically, castor is a triglyceride (ester) of fatty acids. Up to 90% of the fatty acid content of the oil is ricinoleic acid (12-hydroxyoleic acid), an 18-carbon acid having a double bond in the 9-10 position and a hydroxyl group on the 12th carbon. As a result, castor oil and products derived from it are used for numerous industrial products, including bio-based lubricants, paints and coatings, plastics, anti-fungal compounds, and cosmetics. The world market for castor oil is 900 million pounds per year. The United States imports 110 million pounds of castor oil per year. One problem in recent years has been the instability in the supply of castor oil. The major suppliers, India and Brazil, have experienced production problems in recent years.
Although there is demand for a dependable supply of castor in the United States, the castor plant is not cultivated in the U.S. because the castor bean from which the oil is obtained also contains the potent toxin ricin and highly allergenic proteins. While breeding of lower toxin strains has been reported, the toxin and allergenic content of castor remain a problem, and workers who handle castor or castor meal can exhibit severe immune reactions, including debilitating hives and asthma. Modification of castor to lessen the hazardous components and make the castor plant suitable for handling by growers and processors is needed to facilitate re-introduction into the United States and acceptance of this important industrial crop which has both an appreciable domestic market and considerable export potential.
Improvement of castor has been limited to traits available in germplasm; however, castor germplasm is of limited use in reducing toxin and allergen content. What is needed is an ability to genetically transform castor and thereby provide a fundamental means to eliminate the hazardous components from the castor and improve agronomic and other traits of castor plants. However, castor has proven recalcitrant to generation of stably transformed plants (S. M. Molina et al., Plant Physiology 147: 270-272, 1995; M. Sujatha et al., Plant Cell Reports 17: 561-566, 1998), and no such transformation method has been available.
The invention is directed to castor plants and their seeds, transformed with a transgene, capable of expression in the cells of the castor plant.
The ability to genetically transform the castor plant provides the means to develop castor having new traits. Introduction and expression of a transgene in castor can be used to eliminate hazardous components from the castor plant. For example, expression of genes for allergenic and/or toxic components could be blocked by anti-sense RNA inhibition of gene expression or by co-suppression, thereby making it an acceptable crop to grow domestically by reducing the hazards associated with growing and processing castor beans. This ability will facilitate domestic introduction and acceptance of this important industrial crop.
Additionally, due to its unique biochemistry, castor can be engineered to produce novel oils such as fatty acids with other polar functionalities, for example, epoxy fatty acids. The estimated demand for an epoxy oil is 300 million pounds per year.
In accordance with this discovery, it is an object of the invention to provide methods for genetic transformation of castor, for which there is no precedent, to thereby create castor plants and lines having new traits.
Other objects and advantages of the invention will become readily apparent from the ensuing description.